Automatic feed control apparatus for machine tools



Dec 10, 1957 CRANE 2,815,561

AUTOMATIC CONTROL APPARATUS FOR MACHINE TOOLS Original Filod Jan. 31,1,955 2 Sheets-Sheet 1 'MJM Q 3770171 2 .[rdzw Dec. 10, 1957 v R. L.CRANE 2,815,561

AUTOMATIC FEED CONTROL APPARATUS FOR MACHINE TOOLS Original Filed Jan.31, 1955 2 Sheets-Sheet 2 rr" J I if 23 f r-fi Ibbaril. Iran:

United States Patent AUTOMATIC FEED CONTROL APPARATUS FOR MACHINE TOOLSRobert L. Crane, Hopkins, Minn, assignor to Continental Machines, Inc.,Savage, Minn, a corporation of Minnesota 4 Claims. (Cl. 2968) Thisinvention relates to machine tools and refers more particularly to metalcutting band. saws wherein work mounted upon a supporting table is fedagainst a saw band constrained to downward travel through an opening inthe table.

As is customary in machine tools of this type, and especially the largercapacity tools, power means are generally provided to advance the worksupporting table and thereby feed the work to the saw band. One suchpower driven work feeding means is illustrated in Patent No. 2,625,965,issued January 20, 1953, to Continental Machines, Inc. Manual control ofthe power driven work feed is generally provided, but even skilledoperators have found it difficult in the past to maintain the mostefficient and effective rate of work feed. Obviously, the

rate of feed must not be excessive for this places an undue load uponthe saw band often resulting in breakage of the band and untimelywearing of its cutting edge; and less than the correct rate of work feedfails to take full advantage of the capacity of the machine.

The copending application of Robert L. Crane, Serial No. 371,302, filedJuly 30, 1953, now Patent No. 2,754,567 discloses and covers anautomatic control for the power driven work feeding means of such bandsaws, which control is governed by the work feeding pressure upon thesaw band; more specifically by the response of a strain sensitiveelement to deflection of a backup post upon which the element is mountedand which post carries the thrust of the work feeding pressure on thesaw band. The present invention is an improvement upon that control, andaccordingly this application bears a continuation-in-part relationshipto said pending application.

The improvement here presented is also disclosed but not claimed inanother pending application of Robert L. Crane, Serial No. 484,904 filedJanuary 31, 1955 (now a Patent No. 2,774,131), so that the instantapplication bears a divisional relationship to that pending application.

Generally speaking the automatic control of the work feed disclosed inthe aforesaid pending application Serial No. 371,302 (Patent No.2,754,567), and upon which the present invention is an improvement,consists in the provision of a control circuit operable to regulate thespeed of the prime mover or power means used to elfect the work feed, astrain sensitive element mounted upon a deflectable backup which carriesthe thrust of the work against the saw band, and suitableinstrumentalities connecting the strain sensitive element with thecontrol circuit so that the rate of work feed is governed bydeflectionof the backup, which in turn, is a measure of the thrust of the workagainst the saw band. However, in the control system of the aforesaidpending application Serial No, 371,302 (Patent No. 2,754,567), the meansby which the thrust on the saw band was imparted to the deflectablebackup post was fixed to the post and included the saw guide by whichthe saw band is guided as it enters the work zone above the worksupporting table. Consequently, the deflection of the backup postresulted not only from the thrust of the work against the post, but inpart also from the drag of the saw band upon the saw guide since themounting for the backup post is of necessity so located that this dragcreated a turning moment upon the backup post.

With a view toward achieving greater accuracy in the control of themachine, this invention has as its main purpose to provide means wherebyany forces resulting from drag of the saw band upon the saw guide willbe contained and prevented from being imposed upon the deflectablebackup.

More specifically an object of the present invention is to mount the sawguide independently of the backup in a Way which firmly restrains thesaw guide against movement endwise and torsionally of the saw band whilepermitting the saw guide to move freely in the direction the workfeeding thrust is imposed upon the saw band, and further to provide athrust transmitting connection between the thus mounted saw guide andthe deflectable backup which is incapable of transmitting to the backupany forces other than the work feeding pressure on the saw band.

The aforesaid pending application Serial No. 484,904, filed January 31,1955 (Patent No. 2,774,131), discloses but does not claim this manner ofmounting the saw guide and transmitting the thrust to the deflectablebackup.

It has also been found that greater accuracy in the control of the workfeed rate will be attained if the lower saw guide with which band sawsare generally equipped and which is located beneath the work supportingtable, is yieldable in the direction of the thrust applied to the sawband by the work; and accordingly, this invention has as another of itsobjects to so mount the lower saw guide.

As explained in application Serial No. 371,302 (Patent No. 2,754,567),two strain gages of the electromagnetic type sold by the GeneralElectric Co., or the resistance type disclosed in Patent No. 2,292,549,may be mounted back-to-back upon a single deflectable backup in such away that deflection of the backup causes the impedance or resistance ofone of the gages to increase and the impedance or resistance of theother to decrease, or if desired, a single strain gage mounted upon thedeflectable backup may be balanced against a suitable reference unit.The former expedient has the advantage of affording a control current ofgreater magnitude for a given deflection of the backup and with a Viewtoward utilizing this advantage, the present invention has as another ofits objects to provide duplicate backup posts and strain sensitiveelements above and below the work table and so arranged that theireffect produced by deflection of the backups is cumulative.

With the above and other objects in view which will appear as thedescription proceeds, this invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the appended claims, it beingunderstood that such changes in the precise embodiment of thehereindisclosed invention may be made as come within the scope of theclaims.

The accompanying drawings illustrate several complete examples of thephysical embodiments of the invention constructed according to the bestmodes so far devised for the practical application of the principlesthereof, and in which:

Figure l is a diagrammatic perspective view illustrating generally theapplication of this invention to a metal cutting band saw equipped witha hydraulically-powered work table feeding mechanism;

Figure 2 is a circuit diagram of the control for the power feedingmechanism;

Figure 3 is a view at an enlarged scale illustrating the companion upperand lower saw guides and backups of the band saw to better illustratethe invention, and

Figure 4 is a view similar to Figure 3, but illustrating the adaptationof strain sensitive elements or gages mounted on the upper and lowerdefiectable backups.

Referring now particularly to the accompanying drawings in which likenumerals indicate like parts throughout several views, the numeral 5designates the frame of a metal cutting band saw of the type wherein anendless flexible saw band 6 is trained over pulleys (not shown) mountedin the base 7 and head 8 of the frame, to have one stretch of the bandtravel downwardly in a straight line through a slot 9 in a worksupporting table 10. The area above the table 10 and within the throatdefined by the frame of the machine thus constitutes the work zone ofthe machine.

The table 10 is mounted for rectilinear motion in a direction parallelwith its slot 9 to feed work mounted on the table against the frontcutting edge of the saw band which, of course, has'suitable cuttingteeth while the opposite rear edge is smooth and provides a bearingsurface. The advance of the table 'may be effected hydraulically asdiagrammatically illustrated in Figure 1, and as more fully illustratedin Patent No. 2,625,965. In this event, a ram 11 of a hydraulic cylinder12 is connected to the table while the cylinder 12 is secured to thebase of the main frame. The table, therefore, partakes of in and outmovement of the ram produced by hydraulic pressure in one end or theother of the cylinder 12.

The hydraulic feed line' leading to that end of the cylinder 12 to whichfluid must be fed to efiect work feeding movement of the table, has asolenoid responsive control valve 13 connected therein to provide meansfor varying work feed rate.

The saw band is supported against the thrust of the work thereon by anupper defiectable backup 14 located above the work table and hence abovethe work zone, and a lower defiectable backup 15 located below the worktable. These defiectable backups have stiff posts 1616, the upper post16 being rigidly mounted in the head 3 of the machine for verticaladjustment to enable its lower end to be brought down close to the workon the table. The specific structure-by which the upper post 16 is thusvertically adjustably mounted, forms no part of this invention andtherefore has not been shown. However, as indicated in the drawings, themounting means includes a vertically adjustable supporting mem ber 17 towhich the post is solidly fixed. The post 16 of the lower backup neednot be vertically adjusted, hence it is simply fixed toa stationarysupporting member 17' suitably mounted in the base 70f the machine.

The manner in which the thrust imposed upon the saw band by the work istransmitted to the backup posts 16 and 16, constitutes an importantfeature of thisinvention. Thus, in accordance with the invention, thecustomary saw guides indicated generally by the numerals 19 and 19,instead of being fixed to the free ends of the backup posts as has beenthe practice heretofore, are separately mounted for free movementthereof in the direction of the work feeding thrust upon the saw bandand merely bear upon or against the backup posts. The saw guides aresubstantialiy as disclosed in' Patent No. 2,311,426, and hence have apair of angularly disposed guide bars 20 which engage the opposite facesof the saw band, and a roller 21 mounted "with its axis to one-side ofthe path of the saw band and its front face in position to have the backedge of the band ride thereon. Accordingly, when properly mounted, thesaw guides serve to hold the saw band against movement with respectthereto, except its intended linear downward travel, and of courseedgewise forward removal to permit replacement of the band.

To mount the saw guides in the manner contemplated, each is fixed to thefree end of an arm 2222' which extends lengthwise along the back edge ofthe saw band toward the adjacent post support 17-17, and each arm 2222'has a hinged connection 23 with its respective post support. Attentionis directed to the fact that the hinged ends of these arms and theadjacent portions of the supports to which they are hinged, arebifurcated to accommodate the saw band and allow the axes of the hingeconnections 23 to pass through the path of the saw band perpendicularlyto the sides of the band. Accordingly, the points of support for the sawguides lie close to the path of the cutting edge of the saw band so thatlittle or no turning moment is imparted to the saw guides by the drag ofthe saw band thereon, and any of the forces which result from such dragare substantially fully contained within the supporting structure of thesaw guides. Thus the mounting of the saw guides restrains them againstmovement endwise and torsionally with respect to the saw band but leavesthem free to swing rearwardly in response to thrust imposed upon the sawband by the work.

The thrust imposed upon the saw guides in the embodiment of theinvention particularly illustrated in Figure 3 is transmitted to theupper backup 16 through a connection 24 which consists simply of aconical boss 25 projecting from the rear of the arm 22 with its apexbearing against the front face of the backup post at its lower end. Anyequivalent manner of imparting thrust from the arm 22 to'the post 16 maybe employed as long as the resulting connection is capable of applyingthe force which results from the thrust of the work against the sawband, onto the post in a direction substantially transverse to the pathof the saw band while accommodating the needed relative movement betweenthe saw guide and the post.

The thrust thus imparted to the backup post results in deflection of thepost, and this deflection is utilized through the medium of a strainsensitive element 26 mounted upon the post to control the work feedingpressure. As more fully brought'out in the copending application SerialNo. 371,302, filed July 30, 1953 (Patent No. 2,754,567), the specifictype of strain sensitive element or gage employed is not important, andfor purposes of illustration, the electromagnetic type sold by GeneralElectric has been shown on the drawings.

The illustrated strain gage comprises two magnetic poles 27 and 27' bothrigidly bolted to the backup post with an air gap therebetween. One ofthe poles has a coil 28 mounted thereon, and as the air gap between thepoles changes as bylateral'relative movement of the poles, the coilimpedance changes. This changing impedance of the coil is used to effecta change in a control circuit, one embodiment of which isdiagrammatically illustrated in Figure 2. As here shown, the coil 28 ofthe strain gage and a reference coil 29 are connected across oppositecorners Elli-30 of a rectifier bridge circuit 31, in series with theresistance element of a potentiometer 32. The slider of thepotentiometer is connected to one side of an A. C. power source providedby the secondary coil of a transformer 33. The other two corners 34-34of the bridge are respectively connected through capacitors 35-45 withthe opposite side of the transformer secondary. Preferably thetransformer is of'the voltage regulator type so as t'o'minimize theeffects of varying line voltage.

A suitable current responsive instrument 36 is connected acrossthe'corners 34--34' of the bridge to show by-the position of its pointer37 any deviation from a predetermined relationship between the impedanceof the coils 28 and 29. The potentiometer 32 enables the bridge to be sobalanced that when the strain or thrust on the backup support is zero,the pointer 37 is at zero indicating that the current flow during eachhalf cycle through one of the capacitors 35-35, one leg of the rectifierand one of the coils 2829 is the same as that flowing through the othercapacitor, the other leg of the rectifier, and the other coil.

As the backup post upon which the strain gage is mounted is deflected bythe thrust of the work feed against the toothed edge of the saw band,the impedance of the coil 28 changes, and consequently there will be adifferent current flow through each of the capacitors 35--35' and adifferent voltage drop across each. The resulting voltage diiferentialcauses a current to flow through the instrument 36 to swing its pointer37 clockwise across its dial. A capacitor 38 connected across thecorners 34-34 of the bridge smooths out the ripple of the D. C. outputcurrent.

As the pointer 37 swings across the face of its dial it approaches acontact 39 on an adjustable arm 40, and when it engages this contact, anenergizing circuit is completed for an electromagnet 41. Energization ofthis electromagnet closes a switch 42 and this in turn, closes thecircuit for the solenoid valve 13 to efiect closure of the valve andcessation of work feeding movement of the table 10. By virtue of theadjustability of the contact carrying arm 40, the control can beadjusted to maintain an optimum work feed rate, which of course, is justbelow that point at which the thrust upon the saw band exceeds thecritical value.

For convenience, the instrument 36 is preferably mounted upon the head 8of the machine, but the potentiometer 32 and the rectifiers of thebridge circuit are preferably mounted in a cabinet 43, which may belocated wherever convenient.

In that form of the invention illustrated in Figure 3 where only theupper backup post carries a strain gage, the thrust applied to the lowersaw guide 19' is cushioned and prevented from affecting the accuracy ofthe control by virtue of the fact that its arm 22' is yieldingly held inproper position by a spring 44 interposed between the backup post 16'and the arm 22'. The spring 44 is sufiiciently light to preclude havingthe lower backup post take any appreciable amount of the work feedforce. The advantage of this arrangement is that it eliminates the needfor a second strain gage on the lower backup and still permits fairlysensitive feed control.

In the embodiment of the invention illustrated in Figure 4, the straingage and all associated structure is duplicated below the work zone, andaccordingly a second strain gage 26 is mounted upon the backup post 16',but in opposed relation to the strain gage 26 on the upper backup post.Accordingly, the changes in impedance resulting from deflection of thetwo posts are in opposite directions so that the net result iscumulative. With this arrangement, there is no need for a reference coilsince the coils 28 and 28 of the two strain gages may be opposed to oneanother in the bridge circuit in the same manner as were the coils 28and 29 in the circuit hereinbefore described.

It should be understood that where a second strain gage is used in themanner described, that is, mounted upon the lower backup post, suitableprovision must be made for protecting it against metal chips coming incontact with the gage posts and thereby changing the magnetic constantsof the circuit. The lower strain gage must also be protected fromcontact with the liquid coolant used in the operation of the machine,which in time would otherwise injure the insulation on the coil.

From the foregoing description taken in connection with the accompanyingdrawings, it will be readily apparent to those skilled in this art thatthis invention constitutes an important improvement upon the inventionforming the subject matter of the pending application Serial No. 371,302(Patent No. 2,754,567), and that it contributes 6 greatly to thepreciseness of the work which can be performed with a metal cutting bandsaw.

What is claimed as my invention is:

1. The combination with an elongated saw member lengthwise movable alonga defined path, which saw member has cutting teeth along its front edgeand a bearing surface along its back edge, a work holding member adaptedto hold work to be acted upon by the saw member, said members beingrelatively movable to efiect work performing feed engagement between thesaw member and work held by the other member, a deflectable backup tosupport the saw member against the thrust of the work thereon, a primemover having a speed adjusting means and means connecting the primemover with one of said members to effect said relative movement betweenthe saw member and the work holding member, of means to automaticallygovern the operation of the prime mover in accordance with the thrust ofthe work against the saw member comprising a power circuit including astrain sensitive element mounted upon the backup and operable bydeflection of the backup resulting from work feeding pressure upon thesaw member to effect a change in the power output of said circuit andmeans connecting the power output of said circuit to the adjusting meansof said prime mover, characterized by the fact that the means wherebythe work feeding pressure on the saw member is imparted to thedeflectable backup comprises: a saw guide engaging the sides and backedge of the saw member; a thrust transmitting connection between the sawguide and the defiectable backup, said connection being arranged toapply force to the deflectable backup in a direction substantiallytransverse to the path of the band; and means mounting the saw guide forfree movement thereof in the direction of said thrust upon the sawmember but restraining the saw guide against movement lengthwise andtorsionally of the saw member, so that the deflection of the backup andthe consequent response of the strain sensitive element is a measure ofthe thrust of the work against the saw member unaffected by the drag ofthe saw member upon the saw guide, said means comprising a fixedsupport; a part fixed to the saw guide; and a hinge connecting said partwith the fixed support, the axis of the hinge being perpendicular to thesides of the saw member and passing through the path thereof as it movesthrough the saw guide.

2. The combination of claim 1 further characterized by the fact that thedeflectable backup comprises: a post parallel to the saw member andrigidly fixed at one end there of to a solid support spaced asubstantial distance from the saw guide, the thrust transmittingconnection between the saw guide and the backup being at the oppositefree end of said backup post; and further characterized by the fact thatthe mounting for the saw guide comprises an arm fixed to the saw guideand extending therefrom parallel to the saw member and the backup postto a point adjacent to the fixed end of the backup post, and meansfreely pivotally supporting said arm at said point for free swingingmovement about an axis perpendicular to the sides of the saw member andpassing through the path thereof as it moves through the saw guide.

3. The combination of claim 1 further characterized by the fact that theendwise moving saw member moves through a work zone; and by the factthat said deflectable backup, strain sensitive element, saw guide,thrust transmitting connection between the saw guide and backup, and themounting for the saw guide are at one side of the work zone and areduplicated at the opposite side of the work zone, but with the twostrain sensitive elements arranged to oppose one another in theireffect, and with both said elements connected in said power circuit sothat their net effect in said circuit is cumulative.

4. The combination of claim 1 further characterized by the fact that:the work holding member is a horizontal table through which the endwisemoving saw member passes in a straight vertical path; by the fact thatsaid deflectable backup, strain sensitive element, saw guide, thrusttransmitting connection between the saw guide and backup and themounting for the saw guide are located above said table; and furthercharacterized by the provision of a second backup for the saw memberlocated below said table; a second saw guide vengaging the saw memberbelow said table; thrust transmitting means positioned to receive thrustfrom said second saw guide; and spring means interposed between saidthrust transmitting means and said second backup.

UNITED STATES PATENTS Roick July 29,

Tannewitz June 16,

Wilkie Sept. 29,

FOREIGN PATENTS Great Britain Apr. 28,

